ENTOMOSTRACA OF MINNESOTA. 111 
In the previous edition it was suggested that this is but an atavistic 
form of C. pulchellus = C. strenuus, and although Schmeil does not 
accept this suggestion, he adds strong probability to it by noticing 
that the eighth joint of the antenne show indications of subdivision 
and have the armature requisite to correspond with ©. strenuus aftersuch 
division. Against the suggestion he urges, (1) that this form isnotsimply 
found in scattered individuals but in large groups; (2) that there 
seems no sufficient reason for such suppression; (3) that the animal is 
often very large, and we should therefore expect it to attain its full 
development. ‘To these it must be replied (1) that it is very common 
for Copepods of a given stage to be associated almost to the exclusion 
of others, thus the net will sometimes bring in from a given locality 
almost solely half grown Diaptomi where on a previous visit adults 
preponderated; (2) that we know too little of the biology of these ani- 
mals to plead our ignorance as a reason for rejecting what is anatom- 
ically probable; (3) rapid increase in size (unusually rank nutrition) 
may be just a condition for retardation of development, as it often is 
in other groups of crustacea. Questions of this nature demand careful 
and continuous observation and experiment, and should not be arbi- 
trarily closed by a prioré arguments. 
Respecting C. lubbockii Brady, whether it should be considered an 
atavistic form of C. strenuus or of C. bicuspidatus is difficult to say. Its 
brackish habitat speaks strongly in favor of its not being a distinct or 
permanent species. The short first thoracic segment and antennze 
incline me to ally it to the latter species. Specimens sent me by Mr. 
E. A. Congdon of Columbia College, from Long Island, seemed iden- 
tical with C. lubbockii Brady, and if this form cannot be brought into 
relation to a 17-jointed species, Brady’s earlier name should be 
revived. It must be observed, however, that the American specimens 
were within direct influence of the sea. 
*Cyclops serrulatus Fischer. 
PLATES XV, Fias. 8-11; XIX, 2-5; XXVI, Fie. 10; XXIX, Fias, 17-19. 
Fischer 751; Lilljeborg ’53; Clats ’57 and ’63; Sars ’63; Lubbock ’63; Heller 70; Fric 
72; Hoek ‘78; Brady ’78 (serrulatus var. montanus, and serrulatus); Uljanin 
"75; Herrick ’82, and ’84 (serrulatus var. elegans, and serrulatus); Rehberg ’80 
(agilis); Cragin ’83 (pectinifer); Daday ’855 (agilis); Sostaric ’88 (agilis); Thall- 
witz ’90 (agilis); Lande ’90 (agilis); Richard ’91; Schmeil ’91 and ’92; Marsh 
192; Turner ’92. 
The commonest and most abundant species of the Hastern States. 
Cephalothorax oval, compact. Abdomen slender and about three- 
fourths as long as the thorax, cylindrical, suddenly enlarged before 
its union with the thorax. Antenne slender, reaching nearly to the 
